The present invention relates to an additives that enhance mineral acid reactions to produce superior acidic reactions, more particularly, to additives that are not limited to pickling metallic surfaces, but have useful application for increased corrosiveness, reduced reaction time with a base and acid reactions with other non-metallic materials.
The term xe2x80x9cpicklingxe2x80x9d is commonly referred to as an acidic solution that is used for the treatment of metallic surfaces to remove metal oxides or scale. Strong acids, such as hydrochloric, nitric, or sulfonic acid are used either individually or in combination to cleanse or to brighten the surfaces of articles that are made of metal by processes such as casting, forging, flat rolling, extruding, etc.
In one typical application, a pickling bath is used to cleanse a flat rolled steel sheet of its oxide coating by immersing it in an aqueous acidic solution prior to applying a protective coating of tin by a hot dipping process. Other coating processes such as electroplating, electrodeposition, spraying, etc. require prior surface cleaning and conditioning of metallic substrates.
A detailed study of previous art reveals that no prior art considers or even mentions the added use of a depolarizer in a pickling acid additive formulation. Depolarizers are used in electroplating processes to remove undesirable by-products that are formed at the substrate solution interface that significantly inhibit or stop the electroplating reaction.
U.S. Pat. No. 4,132,568, granted Jan. 2, 1979, to D. W. Irwin, discloses an additive to a pickling acid bath to increase its effectiveness when conditioning the surface of a metal being treated. Sodium sulfite is added to the blend to enhance and to stabilize the formation of colloidal sulfite from sodium thiosulfate.
U.S. Pat. No. 3,595,799, granted Jul. 27, 1971, to J. C. Peterson, discloses a picking additive composition, which when added to an acid picking bath, reduces the acid consumption by at least 25%.
U.S. Pat. No. 3,226,180, granted Dec. 28, 1965, to J. T. Irwin, teaches a process for conditioning metal surfaces in an acid pickling bath, containing preferably sodium thiosulfate, capable of releasing colloidal sulfur and an organic picking acid inhibitor, diorthotolythiourea.
U.S. Pat. No. 2,831,814, granted Apr. 22, 1958, to A. E. Chester and J. T. Irwin, relates of an acid pickling bath, used for the surface treatment of ferrous metals, containing a compound, sodium thiosulfate and a water soluble ionizable ferrocyanide, preferably sodium ferrocyanide. The sodium thiosulfate is capable of releasing colloidal sulfur.
U.S. Pat. No. 2,692,188, granted Oct. 19, 1954, to A. E. Chester and J. T. Irwin, discloses an acid pickling composition and method of picking steel, containing a compound, sodium thiosulfate, that is capable of releasing colloidal sulfur and a water soluble ionizable inhibitor, sodium thiosulfate, to produce a microfine etch.
U.S. Pat. No. 2,692,187, granted Oct. 19, 1954, to A. E. Chester and J. T. Irwin, discloses an acid pickling composition and method of pickling steel containing a compound, sodium thiosulfate, that is capable of releasing colloidal sulfur and a water soluble chromic inhibitor, chromium aldonate, to produce a microfine etch for better adherence of other electrodeposited metals.
U.S. Pat. No. 2,636,009, granted Apr. 21, 1953, to J. T. Irwin, relates to the conditioning of metal surfaces where the pickling acid bath is comprised predominantly of sulfuric acid, with 1 to 8 parts of sodium thiosulfate per seven hundred parts of seven percent of sulfuric acid.
The use of sodium thiosulfate and sodium sulfite is not new, having been previously disclosed. Additives to mineral acids in the form of inhibitors to retard corrosion rates or in the form of protective coatings to prevent corrosion are common. Additives in the form of wetting systems, sophisticated or simpler are also used in manufacturing processes using mineral acid to wet out the acid or form a blanket of foam to hold down dangerous acid fumes. These various chemicals can be added at the point of manufacture or to the manufacturing process involving the acid.
However, the use of sodium thiosulfate for treatment of a mineral acid to improve quality thereof by directly adding the thiosulfate to a commercial grade of acid imparts a significant problem. The sodium thiosulfate will breakdown into an undesirable cloud of sulfur when directly added to the commercial grade acid.
It is therefore an object of the present invention to add in small, incremental doses, a blend of sodium thiosulfate and a depolarizer, trisodium phosphate, ranging from 0.01% to 5% by weight of acid, to change the properties of a mineral acid making it more active in its ability to react with and dissolve certain metals, oxides, and salts.
It is another object of the present invention to use a blend of sodium salts and phosphates at various delivery points to change the properties of a mineral acid, thereby enhancing its ability to react with oxides, bases, or alkali""s to form salts.
It is still another object of the present invention to use a blend of sodium salts and phosphates to modify the properties of a mineral acid, so that it will corrode metal at a faster rate.
It is still yet another object of the present invention to use a blend of sodium salts and phosphates to modify the properties of a mineral acid, that once modified by using the formulation herein disclosed, will react with various salts at a faster rate.
These and other objects and advantages of the present invention will be better appreciated and understood upon reading the following detailed description of the formulation described herein as the presently preferred embodiment.
The present invention relates to enhancing the reactivity of an inorganic acid, commonly referred to as mineral acid or acid salt, by adding a novel formulation of sodium thiosulfate, sodium sulfite, and trisodium phosphate. This novel formulation enhances the corrosion properties of a mineral acid to produce a superior acid reaction when measured in terms of corrosiveness or reactivity of the substrate.
This invention incorporates the known acid enhancing compounds, sodium thiosulfate and sodium sulfite, with trisodium phosphate as a direct addition to the mineral acid at any one of several delivery points to change the properties of that mineral acid making it more active as a means of reacting with and dissolving certain metals, salts, and oxides.
Such treatment of an acid using the formulation of the present invention may take place after the manufacture of an acid, in storage, or prior to shipment to the end user; to a mineral acid which has been processed through an acid recovery system, or to a mineral acid as it is being used in a manufacturing process.
An inorganic acid is often referred to as being a mineral acid. The two major types of mineral acid that are most often used are sulfuric and hydrochloric acid. Each mineral acid has it own unique properties and is blended in various commercial grades for industrial consumption.
By itself, mineral acid of a known concentration will exhibit reactivity or corrosive properties with various metals, salts, and oxides that can be measured and compared with the objects of the present invention.
The following examples illustrate that a mineral acid can be so modified to corrode metal at a faster rate and that a mineral acid once modified by using the concepts herein disclosed will react with a base at a faster rate. The examples that follow will show reactions of the sodium thiosulfate and trisodium phosphate in a mineral acid singly and in combination to better illustrate the advantages of the present invention.
The pickling additive of the preferred embodiment of the present invention is comprised of the following formula relationship. The formula relationship of sodium thiosulfate to trisodium phosphate to sodium sulfite ranges from 0.1% wt. to 20% wt. sodium thiosulfate to 0.001% wt to 10% wt trisodium phosphate to 0.02% wt. to 4% wt. sodium sulfite, and the remainder, water. Other combinations within the ranges of these chemicals may be employed to maximize the effect of the acid reaction but for purposes of illustration a typical additive, Blend A, to be blended with an acid such as sulfuric or hydrochloric, but not limited to these mineral acid""s would be: 10.0% wt. trisodium phosphate, 9.0% wt. sodium thiosulfate, 0.5% wt. sodium sulfite and 80.5% wt. water.
In an alternative composition Blend B additive is preferably 14% wt. sodium thiosulfate, 1.4% wt. sodium sulfite, 1% wt. trisodium phosphate and the balance, water. Blend B contains a 30% wt. reduction in sodium thiosulfate, yet the reaction times are faster when compared to that of trisodium phosphate alone or sodium thiosulfate/sodium sulfite alone.
This invention is further illustrated in the following examples.